The present invention relates generally to the field of digital computers, and, in particular, relates to apparatus for controlling computer graphics displays.
Multiprocessing graphics workstations known in the art have the capability to run several applications or display different images concurrently. Such multiprocessing graphics workstations typically employ bitmap planes with per-screen control information, rather than color information, as a general mechanism to support per-screen video display mode specification. Display modes include selecting false color or real color, or using particular sections of a color lookup table.
The high cost of bitmap memory and the difficulty in achieving very fast memory cycle times in physically large RAM arrays has limited the resolution and plane count provided by bitmaps. "False color" configurations having four, eight or twelve planes have become a popular compromise between the cost of deep bitmaps and the desire for realistic colors. In a false color mode, all three red, green and blue (RGB) lookup tables (LUTs) receive data values from the same planes. In a real color mode, three sets of planes are used, with each set routed to a single LUT.
Recently, as RAM densities have soared, bitmap resolution and plane count have increased. 1-MByte and 4-Mbyte Video RAMs will continue this trend. Color lookup tables have also grown as static RAM density improves. Greater resolution has allowed engineering graphics workstations to usefully display multiple images or contexts on the same screen, and additional planes and larger lookup tables have presented the opportunity to interpret the bitmap in a variety of ways. A deficiency associated with per-screen display mode specification, typical of conventional graphics display systems, however, is that the entire screen is typically interpreted using one display mode.
Typically, a twenty-four plane configuration workstation must run real color, false color, and even monochrome graphics applications, some of which double-buffer images or reload color lookup tables. Since the display must be reconfigured or the lookup table altered for each, these applications cannot share the screen in conventional graphics display systems. Such whole-screen reconfiguration conflicts with the capability of multiprocessing workstations to use windows to share the screen among applications.
There is thus a conflict between the paradigm in multiprocessing workstations wherein the screen is composed of windows or images belonging to several independent contexts and the single screen-wide display interpretation mode such windows must share in conventional graphics systems.
If such mode information could be associated with windows or pixels rather than the whole screen, each application or image could define modes independently, and applications could share the screen more effectively.
If pixels can select by which "configuration" they are interpreted, then different windows can be displayed as needed without conflicts. For example, the pixels in one window could be marked as "twenty-four plane real color", whereas another window could be "eight-plane false color". Moreover, pixels in one window could be marked for a "fast clear mode" so as to reduce the time required to clear a window. The screen-wide display mode could be replaced by per-pixel display mode specification. Although commonly such specification will vary on a per-window basis, per-rectangle sub-windows, per-object, and even per-pixel variation would also be useful.
It is thus an object of the invention to provide an improved computer graphics display controller system.
It is a further object of the invention to provide a computer graphics display controller system which allows for flexible configuration of an image memory.
It is another object of the invention to provide a computer graphics display controller system in which the mode or configuration by which pixels are interpreted can be flexibly varied across a display screen.
It is a further object of the invention to provide a computer graphics display controller system which supports a per-pixel display mode specification.
It is yet another object of the invention to provide a computer graphics display controller system which allows faster dynamic displays by reducing the time required for clearing a new buffer.